The number of natural numbers smaller than `10^4` of which all digits are different, is

The number of natural numbers less than 1000, in which no two digits are repeated is

The total number of eight digit numbers in which all digits are different, is

The number of natural numbers of two or more than two digits in which digits from left to right are in increasing order is

Find the number of natural numbers which are less than 2xx10^8 and which can be written by means of the digit 1 and 2.

Find the number of natural numbers which are less than 2xx10^8 and which can be written by means of the digit 1 and 2.